Clean up cert checks and cert tests

[nephomaniac]

Suggesting the following:
-Check the actual Euca property for a cert limit (might be an assumption of '2' used today).
-If the euca property is not available to this user, try to create a cert, catch failure.
-Log warning/error level message instead of raising an exception.
-Add info about which euca property can be used to change/increase the limit if the test is unable to create or find an existing/active cert.
-Make cert usage option for image suite(s)
-Add cert params/cli-args to tests which may use them

[vasiliykochergin]

Fantastic idea! +1