Volumes: strict type and value check of the 'bootable' flag

Reverts Iffe5d380410f5c698018a5c3106c99af05f0b80d. It is reverted because 
Iffe5d380410f5c698018a5c3106c99af05f0b80d was a workaround for bug #1227837
that is now fixed. So we can safely revert the workaround.

Change-Id: I9430b14a56958169d9638e6abee2206bbda99d43
1 file changed