Unhardcoded logging level for syslog in Libvirtd (nova-compute)

This patch unhardcodes syslog parameters for libvirtd and qemu in libvirtd.conf
and libvirtd.conf templates accordingly. These parameters might be configured using
the bellow pillar structures:

  nova:
    compute:
      libvirt:
        logging:
          level: 3
          filters: '3:remote 4:event'
          outputs: '3:syslog:libvirtd'
          buffer_size: 64
      qemu:
        logging:
          handler: logd
      virtlog:
        enabled: true
        level: 3
        filters: '3:remote 4:event'
        outputs: '3:syslog:virtlogd'
        max_clients: 1024
        max_size: 2097152
        max_backups: 3

Change-Id: Ic8b3f9ab1e55d9b972ff3baff48312e4dea8a5e5
Related-PROD: PROD-19919
diff --git a/README.rst b/README.rst
index bf4cbe2..9af981f 100644
--- a/README.rst
+++ b/README.rst
@@ -772,6 +772,95 @@
           <logger_name>:
             level: WARNING
 
+Configure syslog parameters for libvirtd
+----------------------------------------
+
+To configure syslog parameters for libvirtd the below pillar structure should be used with values which are supported
+by libvirtd. These values might be known from the documentation.
+
+ nova:
+   compute:
+     libvirt:
+       logging:
+         level: 3
+         filters: '3:remote 4:event'
+         outputs: '3:syslog:libvirtd'
+         buffer_size: 64
+
+#################################################################
+#
+# Logging controls
+#
+
+# Logging level: 4 errors, 3 warnings, 2 information, 1 debug
+# basically 1 will log everything possible
+#log_level = 3
+
+# Logging filters:
+# A filter allows to select a different logging level for a given category
+# of logs
+# The format for a filter is one of:
+#    x:name
+#    x:+name
+#      where name is a string which is matched against source file name,
+#      e.g., "remote", "qemu", or "util/json", the optional "+" prefix
+#      tells libvirt to log stack trace for each message matching name,
+#      and x is the minimal level where matching messages should be logged:
+#    1: DEBUG
+#    2: INFO
+#    3: WARNING
+#    4: ERROR
+#
+# Multiple filter can be defined in a single @filters, they just need to be
+# separated by spaces.
+#
+# e.g. to only get warning or errors from the remote layer and only errors
+# from the event layer:
+#log_filters="3:remote 4:event"
+
+# Logging outputs:
+# An output is one of the places to save logging information
+# The format for an output can be:
+#    x:stderr
+#      output goes to stderr
+#    x:syslog:name
+#      use syslog for the output and use the given name as the ident
+#    x:file:file_path
+#      output to a file, with the given filepath
+# In all case the x prefix is the minimal level, acting as a filter
+#    1: DEBUG
+#    2: INFO
+#    3: WARNING
+#    4: ERROR
+#
+# Multiple output can be defined, they just need to be separated by spaces.
+# e.g. to log all warnings and errors to syslog under the libvirtd ident:
+#log_outputs="3:syslog:libvirtd"
+#
+
+# Log debug buffer size: default 64
+# The daemon keeps an internal debug log buffer which will be dumped in case
+# of crash or upon receiving a SIGUSR2 signal. This setting allows to override
+# the default buffer size in kilobytes.
+# If value is 0 or less the debug log buffer is deactivated
+#log_buffer_size = 64
+
+To configure logging parameters for qemu the below pillar structure and logging parameters should be used:
+
+ nova:
+   compute:
+      qemu:
+        logging:
+          handler: logd
+      virtlog:
+        enabled: true
+        level: 4
+        filters: '3:remote 3:event'
+        outputs: '4:syslog:virtlogd'
+        max_clients: 512
+        max_size: 2097100
+        max_backups: 2
+
 Inject password to VM
 ---------------------