1.1 requires setting a Perforce password breaking Perforce setup for external authentication

checkin r654744 for SCM-363 introduces a requirement to set a Perforce password.
This will break the SCM provider when Perforce is configured to not accept a password. This will be the case when using the OS security instead of Perforce' own.
The SCM pluging throws an exception when not providing a password, Perforce throws an error when trying to login with a (dummy) password.

When no username and/or password is provided, the Perforce login step should be skipped.

=========
Perforce login output when running p4 from the command prompt:
p4 login
'login' not necessary, no password set for this user.

p4 login john
You don't have permission for this operation.

=========

Offending code:
PerforceLoginCommand.java

if ( StringUtils.isEmpty( repo.getPassword() ) )

{ throw new ScmException( "password is required for the perforce scm plugin." ); }