Add NOVACLIENT_BYPASS_URL env variable

Currently, in order to use a bypass URL, you need to specify it using the
`--bypass-url` command-line option each time, which is inconvenient if you
plan on always using a bypass URL.

This patch adds a `NOVACLIENT_BYPASS_URL` environment variable which can be
placed in the `novarc` to persistently set this option.

Change-Id: I49e67ee1fc3570a43e49dc1d78d8ca0b26945bc8
Closes-Bug: 1326134
Merge "Add NOVACLIENT_BYPASS_URL env variable"