Clean up import of cinderclient exceptions

Clean up import of cinderclient exceptions

Don't import a particular version of the cinderclient API - just import the
client module and pass the version we want to the Client() constructor as
is intended. This allows up to access the exceptions directly through
client.exceptions, rather than having to do a separate import.

Change-Id: Ic0e47506a51a572da01fdfdef0367cfdb3e34d54