Liang SHANG

Results 4 issues of Liang SHANG

Firstly list the pros and cons of changing package dependency management from Dep to Go Modules.

switch.go has different logger lib. Unify the logger libs.

remove pmm-client and pmm-server dependencies to boost image build

When `make docker-image` is run, gcc:8.0 is started, followed by golang1.11.0, and then mysql:5.7.22 is used to build the final image. Can we use multi-stage build to simplify?