22134: Define PATH in nginx+Passenger configuration

22134: Define PATH in nginx+Passenger configuration

RailsAPI needs this set to run `arvados-server`. To date this has been
handled by the default `passenger_load_shell_envvars on`, which starts
RailsAPI via `bash -l -c` to load environment variables from the shellrc
files in /etc. However, this can fail due to system configuration
changes, and we have seen Passenger try to start RailsAPI with an empty
PATH after a server reload/restart. Defining PATH here should make the
system more resilient against other system configuration changes.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>