Before this commit, provisioning was done by executing provision.py,
which printed the log directly to stdout, making debugging harder.
This commit creates a wrapper bash script 'provision' in tools, which
calls 'zulip/scripts/tools/provision_vm.py' (the new location of
provision.py) and prints all the output to
'zulip/var/log/zulip/zulip_provision.log' via 'tee'.
Travis tests and docs have been modified accordingly.
Previously, we got the following as a part of the output when running
`tools/run-dev.py` without provisioning:
It looks like you checked out a branch that has added
dependencies beyond what you last provisioned. Your tests
are likely to fail until you add dependencies by provisioning.
which is a bit confusing.