Move bpglob out of ToolDir

ToolDir is going to become unstable when switching between KatiEnabled
and Soong-only builds while the duplication between out/soong/host and
out/host is resolved.  bpglob gets executed very early during bootstrap,
before the primary builder has run to update the paths to match the
current configuration.  Move it into SoongOutDir() so that its path
is more stable.

Moving bpglob causes incremental build issues, so add a bootstrapEpoch
constant that can be changed when making incompatible changes and will
wipe bootstrap intermediates.

Bug: 204136549
Test: m nothing
Change-Id: I7b1bd1ebfe1209d11db691b3ee00873ef92658cd