Revert "build: Removes introspection.m4, which is already provided by aclocal"

This reverts commit 16d819a09e01a7832aad15ebfe7ea6e30344fcdb.

Seems that distcheck target requires this file. Reverting
Implements EvdTransport's interface method open() in EvdWebsocketServer
tests: Runs EvdResolver error test only if slow tests are enabled
tests: Removes commented code from resolver and websocket transport tests
Adds CONSTRUCT_ONLY flag to 'address' property of EvdConnectionPool
build: Fixes tests data dir path to consider non-standard build prefixes