This change has two major parts, which were interwoven enough to do
them in one change:
1) make serverinit.Config fully opaque, in prep for TOML configs #1134
2) shrink the massive server/perkeepd/camlistored.go file. It was out
of control and had a bunch of code that better belonged
elsewhere. This change moves a few hundred lines of code from
camlistored.go into more logical places: internal/osutil/gce for
GCE stuff, serverinit for config stuff (KeyRingAndId), etc.
I also added a TODO to make it possible to compile perkeepd without
any GCE stuff, which I saw as a possible and worthy goal only after
moving everything away.
Updates #1134
Change-Id: Iea6f84c5aca9c70b97806f4a201ec35e0f630e3b
Brad Fitzpatrick