Fix incorrect certificate handling on Windows

Summary:

This reimplements suvayu/electrum-personal-server#1 such that it works
on Windows properly, see: chris-belcher#44.
The certificates are now treated as package_data, and are accessible
using the pkg_resources API.  All other behaviour is same as "Handle
certificate files in a more robust manner".

Author: suvayu

MANIFEST.in

@@ -1,4 +1,4 @@
 include README.md
 include doc/*.md
-include certs/*
+include electrumpersonalserver/certs/*
 include config.cfg_sample

electrumpersonalserver/__init__.py

@@ -1,5 +1,5 @@
 import electrumpersonalserver.bitcoin
 import electrumpersonalserver.server
 
-__certfile__ = 'etc/electrum-personal-server/certs/cert.crt'
-__keyfile__ = 'etc/electrum-personal-server/certs/cert.key'
+__certfile__ = 'certs/cert.crt'
+__keyfile__ = 'certs/cert.key'

certs/cert.crt electrumpersonalserver/certs/cert.crt

@@ -468,19 +468,17 @@ def get_scriptpubkeys_to_monitor(rpc, config):
     return False, spks_to_monitor, deterministic_wallets
 
 def get_certs(config):
-    from pathlib import Path
-    import electrumpersonalserver
+    from pkg_resources import resource_filename
+    from electrumpersonalserver import __certfile__, __keyfile__
     logger = logging.getLogger('ELECTRUMPERSONALSERVER')
     certfile = config.get('electrum-server', 'certfile', fallback=None)
     keyfile = config.get('electrum-server', 'keyfile', fallback=None)
     if (certfile and keyfile) and \
        (os.path.exists(certfile) and os.path.exists(keyfile)):
         return certfile, keyfile
     else:
-        # platform independent top directory
-        top = Path(os.path.dirname(electrumpersonalserver.__file__)).parts[:-4]
-        certfile = os.path.join(*top, electrumpersonalserver.__certfile__)
-        keyfile = os.path.join(*top, electrumpersonalserver.__keyfile__)
+        certfile = resource_filename('electrumpersonalserver', __certfile__)
+        keyfile = resource_filename('electrumpersonalserver', __keyfile__)
         if os.path.exists(certfile) and os.path.exists(keyfile):
             logger.info('using cert: {}, key: {}'.format(certfile, keyfile))
             return certfile, keyfile

certs/cert.key electrumpersonalserver/certs/cert.key

@@ -16,8 +16,8 @@
             "electrum-personal-server-rescan = electrumpersonalserver.server.common:rescan",
         ]
     },
+    package_data={"electrumpersonalserver": ["certs/*"]},
     data_files=[
-        ('etc/electrumpersonalserver/certs', ['certs/cert.crt', 'certs/cert.key'])
         ("etc/electrum-personal-server", ["config.cfg_sample"]),
         ("share/doc/electrum-personal-server", ["README.md"]),
     ],