Add Password parameter, and change Test-TargetResource to match the Subj...

Add Password parameter, and change Test-TargetResource to match the Subject name, instead of looking for equal to.

This has been tested on Windows 2008R2 and 2012R2.
CertUtil (Win2008) requires a clear text password, and Import-PFXCertificate requires a SecureString for password.
So the choice is to pass in a clear text password in $Password, then convert to SecureString. Or pass in a SecureString and decrypt to get the clear text.