FMS: add a global transfer timeout parameter

Since scp and rsync have unlimited timeout,
we allow users to define a global timeout parameter (default: 0/unlimited)
fixes #396
FMS: set default global transfer timeout parameter value
FMS: add documentation for VISHNU_TRANFER_TIMEOUT option
UMS: register VISHNU_TRANSFER_TIMEOUT option and value check
database: add migration script (new default vishnu option)