Allow for a 4 char suffix on the end of hostnames

[nkinkade]

As we migrate cloud deployments to use a load balancer backed by managed instance groups, we can no longer count on machine names to be predetermined. MIG instances have a "-<4 char>" suffix, and are managed by the instance group, not M-Lab. In order to support this use case, the changes in this PR allow for a suffix to be part of the hostname without failing Parse(). Callers can use the suffix, if found, or not.

---

This change is 

[coveralls]

Pull Request Test Coverage Report for Build 1213

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.08%) to 94.347%

---

Files with Coverage Reduction	New Missed Lines	%
logx/logx.go	2	96.0%
<!--	Total:	2		-->

Totals
Change from base Build 1208:	-0.08%
Covered Lines:	2153
Relevant Lines:	2282

---

💛 - Coveralls