Add serval_maps_push.sh script

To be used as the --exec-on-unpack option to rhizome_mirrord

Rsyncs all the unpacked zip files to the Serval Maps testing server and fetches
the Serval Maps re-scan URL

Is invoked with arg1 = path of unpack directory, args2..N = names of newly
unpacked directories within arg1

If the RHIZOME_MIRRORD_LOG_STDOUT env var is set, then enables shell execution
tracing