Add module based host-tools snapshot

Add new module:
host_snapshot {
    name: "host-snapshot"
    deps: [
      (list of host tools)
    ],
    ...
}

Package host tools using android.PackagingBase to capture host tools and transitive packaging data.
Add JSON meta data to snapshot that allows snapshot to be installed via development/vendor_snapshot/update.py

Add support to generate a fake host snapshot of all host modules that is used to detect required
modules via development/vendor_snapshot/update.py.

Bug: 192556798
Bug: 194799048
Bug: 192896149
Test: m HOST_FAKE_SNAPSHOT_ENABLE=true host-fake-snapshot dist -- check snapshot exists in dist

Change-Id: I849c4db801cd858408f6fe6a3ce69262a23a5be9

python/python.go

@@ -310,13 +310,16 @@ func versionSplitMutator() func(android.BottomUpMutatorContext) {
 // HostToolPath returns a path if appropriate such that this module can be used as a host tool,
 // fulfilling HostToolProvider interface.
 func (p *Module) HostToolPath() android.OptionalPath {
-	if p.installer == nil {
-		// python_library is just meta module, and doesn't have any installer.
-		return android.OptionalPath{}
+	if p.installer != nil {
+		if bin, ok := p.installer.(*binaryDecorator); ok {
+			// TODO: This should only be set when building host binaries -- tests built for device would be
+			// setting this incorrectly.
+			return android.OptionalPathForPath(bin.path)
+		}
 	}
-	// TODO: This should only be set when building host binaries -- tests built for device would be
-	// setting this incorrectly.
-	return android.OptionalPathForPath(p.installer.(*binaryDecorator).path)
+
+	return android.OptionalPath{}
+
 }
 
 // OutputFiles returns output files based on given tag, returns an error if tag is unsupported.