Fix *-paladin --buildbot --debug testing.
Fix *-paladin --buildbot --debug testing.

Forcing /b/archive is unfriendly for developer systems; if we're
in debug mode, then use the trybot root.

This approach's basically been broken from day1, but recently
flaired via I3fe28e moving it, thus fixing the --debug case
fully this time around.

BUG=chromium-os:30187
TEST=sudo rm -rf /b/; \
     cbuildbot x86-generic-paladin --buildbot --debug <args>
     works again.

Change-Id: I884fa61bc98ea3d4a5a07e1237bc6d1f10b649bf
Reviewed-on: https://gerrit.chromium.org/gerrit/22560
Commit-Ready: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Reviewed-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>
Tested-by: Brian Harring <fdc2d0a2e2340b623587cee5ea8dff425d1eb1f3@chromium.org>

bpsinc-native/src_third_party_chromite,coreos/chromite,coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,coreos/chromite,chadversary/chromiumos.chromite