Low: libcrmcommon: Standardize remote environment variable parsing

Our bespoke code has been fragile and hard to understand at a glance.
There were certainly corner cases involving nested quotes that were not
handled in the way the shell would handle them.

Now we use g_shell_parse_argv() instead, to mimic how the shell would
process the value in a "NAME=VALUE" assignment statement.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>