R1:6bac7e390e5b

Move "send test" to bin/mail

Summary: Like D6417. See D6413.

Test Plan:
>>> orbital ~/devtools/phabricator $ echo "hello" | ./bin/mail send-test --to dog --cc duck --from epriestley --subject 'hey there' --attach README --tag blip --tag bloop
Reading message body from stdin...
Mail sent! You can view details by running this command:

phabricator/ $ ./bin/mail show-outbound --id 6480

>>> orbital ~/devtools/phabricator $ ./bin/mail show-outbound --id 6480
PROPERTIES
ID: 6480
Status…