Fix 1105

[vernondcole]

What does this PR do?

• Completes the correction of Only overwrite the minion config file if '-C' is passed. Otherwise, preserve it. #848
• update the Ubuntu version in the Vagrantfile to a supported release.

What issues does this PR fix or reference?

#1105

Previous Behavior

salt-bootstrap.sh -F caused overwrite of the minion config, but not the keys.

sh salt-bootstrap.sh failed with

 $ sudo sh salt-bootstrap.sh -A salt.2txt.us -i sb1
 *  INFO: Running version: 2017.05.24
 *  INFO: Executed by: sh
 *  INFO: Command line: 'salt-bootstrap.sh -A salt.2txt.us -i sb1'
 *  WARN: Running the unstable version of bootstrap-salt.sh

 *  INFO: System Information:
 *  INFO:   CPU:          GenuineIntel
 *  INFO:   CPU Arch:     x86_64
 *  INFO:   OS Name:      Linux
 *  INFO:   OS Version:   3.2.0-126-virtual
 *  INFO:   Distribution: Ubuntu 12.04

 * ERROR: End of life distributions are not supported.
 * ERROR: Please consider upgrading to the next stable. See:
 * ERROR:     https://wiki.ubuntu.com/Releases

New Behavior

• Key files will be replaced, too.
• Can actually test using Vagrant

[vutny]

Good job @vernondcole !

Since passing -C (config only) option implies -F (forced overwrite), this is backwards compatible and more useful.

[rallytime]

@vernondcole Yes, this is the right way to do this. Thank you for fixing this!