provision: Improve error messaging when attempting to use Ubuntu Trusty.
provision: Improve error messaging when attempting to use Ubuntu Trusty.

As part of dropping support, we add appropriate error messaging when a
user attempts to provision while using trusty.  If the user is running
in Vagrant we append information on how to proceed.

timabbott/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,shubhamdhama/zulip,tommyip/zulip,punchagan/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,shubhamdhama/zulip,punchagan/zulip,andersk/zulip,tommyip/zulip,shubhamdhama/zulip,eeshangarg/zulip,brainwane/zulip,rishig/zulip,andersk/zulip,brainwane/zulip,synicalsyntax/zulip,rht/zulip,rishig/zulip,kou/zulip,brainwane/zulip,tommyip/zulip,showell/zulip,andersk/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,synicalsyntax/zulip,rishig/zulip,kou/zulip,andersk/zulip,timabbott/zulip,andersk/zulip,eeshangarg/zulip,shubhamdhama/zulip,brainwane/zulip,synicalsyntax/zulip,timabbott/zulip,hackerkid/zulip,kou/zulip,rht/zulip,showell/zulip,showell/zulip,kou/zulip,shubhamdhama/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,zulip/zulip,tommyip/zulip,timabbott/zulip,rishig/zulip,rishig/zulip,hackerkid/zulip,tommyip/zulip,shubhamdhama/zulip,synicalsyntax/zulip,hackerkid/zulip,zulip/zulip,shubhamdhama/zulip,punchagan/zulip,punchagan/zulip,punchagan/zulip,timabbott/zulip,punchagan/zulip,eeshangarg/zulip,timabbott/zulip,brainwane/zulip,zulip/zulip,brainwane/zulip,hackerkid/zulip,tommyip/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,kou/zulip,showell/zulip,rishig/zulip,tommyip/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,eeshangarg/zulip,rishig/zulip,punchagan/zulip,synicalsyntax/zulip,brainwane/zulip,timabbott/zulip,andersk/zulip,showell/zulip,zulip/zulip,zulip/zulip