Use a single keypair for multiple instances

When I ran manila scenario tests, some tests failed due to
ssh key authentication. I noticed that tests with single
instance pass, however, tests with more than one instance
(e.g. "test_read_write_two_vms" test) fail.
I figured out that every instance initialization creates a
unique keypair.
An unnecessary resource duplication, when a single user boots
more than one instance. Depending on test flow this may also
cause keypair mismatch.

Change-Id: Ic685d1b9574daf7e6c9b90d5636f1b614a70b0da
Related-bug: #1858024
2 files changed