vtpmmgr: Fix owner_auth & srk_auth parsing

vtpmmgr: Fix owner_auth & srk_auth parsing

Argument parsing only matches to before ':' and then the string with
leading ':' is passed to parse_auth_string which fails to parse.  Extend
the length to include the seperator in the match.

While here, switch the seperator to "=".  The man page documented "="
and the other tpm.* arguments already use "=".  Since it didn't work
before, we don't need to worry about backwards compatibility.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>