Fix metsrv.dll name issue

As mentioned here https://community.rapid7.com/thread/3788 the metsvc
script was still looking for the old file name for metsrv.dll, which
was causing the script to fail.

This commit fixes this issue. A hash is used to indicate local and remote
file names so that the remote can continue to use metsrv.dll, but it
is correctly located on disk locally.
Land #2707 - Fix metsrv.dll name issue in metsvc script

[FixRM #8707]