Fix in url parser after go 1.12.8

[wayjam]

Description

Fix net/url.Parse no longer works for dsn string with port after go 1.12.8

parse mysql://user@tcp(localhost:3306)/boulder_test?parseTime=true: invalid port ":3306)" after host

Releated issue: golang/go#33646

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README.md / documentation, if necessary
• Added myself / the copyright holder to the CONTRIBUTORS file

[wayjam]

@phogo-bot @Svett

[iamralch]

@wayjam Thanks for the PR. I will review it soon. It looks like that my github notification settings were not correct. So I didn't see the PR earlier. Sorry about that.

[iamralch]

Please address the cases that I have concerns.

[iamralch]

Thanks for contribution! I will schedule release by the end of this week.