Speed up LTM server launch by combining the files read from GCS

[tytso]

The shell script /usr/local/lib/gce-fetch-gs-files takes 20 seconds to run:

Jun 04 21:18:34 xfstests-ltm systemd[1]: Starting GCE self-signed cert fetch from GCS...
Jun 04 21:18:44 xfstests-ltm root[1841]: fetching cert completed, gsutil returned 0
Jun 04 21:18:50 xfstests-ltm root[2213]: fetching config completed, gsutil returned 0
Jun 04 21:18:54 xfstests-ltm systemd[1]: Started GCE self-signed cert fetch from GCS.'

This is because it calls gsutil multiple times --- and each run takes a few seconds. It should be possible to combine the files needed to configure the LTM server into a single tar file.