--gssapiServiceName should not require --gssapiHostName in the tools

A recent user of mongodump found that setting -gssapiServiceName did not seem to change the service name which the driver was trying to acquire a ticket for. When passing '-gssapiServiceName mockservice', the following error was still produced:

generic failure: GSSAPI Error: Unspecified GSS failure.  Minor code may provide more information (Server mongodb/localhost@LDAPTEST.10GEN.CC not found in Kerberos database)

Adding --gssapiHostName caused the tool to attempt to acquire the correct service principal.

These properties should be able to be set independently, as in the shell.