Support harbor with self-signed certification

[cdan]

When config Image in yaml with self-signed registry, like "192.168.1.100/test/test-image", the builder POD will fail to start with error "[prepare] prepare:main.go:79: Get https://192.168.1.100:443/v2/: x509: certificate signed by unknown authority".

[zhouguangming]

how did you solve this issue ? @cdan

[sukhil-suresh]

There are workarounds discussed on this similar issue - #207