Update Alpine mirrors to avoid build failures
Update Alpine mirrors to avoid build failures

The default Alpine mirror (dl-cdn) is known not to always work,
like in my case where apk installs have been failing for hours
throwing "protocol error" messages.

This commit updates the mirror to a new reliable mirror which
works well enough and does not cause random ambassador container
image build failures.

datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador