Use compile-time paths in the manual pages

Replace the hard-coded paths for various BIND 9 files (configuration,
pid, etc.) in the man pages and ARM with compile-time values using the
sphinx-build replace system.

This is more complicated, because the restructured text specification
doesn't allow |substitions| inside ``code-blocks``, so for each specific
file we had to create own substition which is sub-optimal, but it is
only way how to do this without adding Sphinx extension.

doc/arm/conf.py

@@ -178,3 +178,17 @@ latex_documents = [
     ]
 
 latex_logo = "isc-logo.pdf"
+
+#
+# The rst_epilog will be completely overwritten from the Makefile,
+# the definition here is provided purely for situations when
+# sphinx-build is run by hand.
+#
+rst_epilog = """
+.. |rndc_conf| replace: ``/etc/rndc.conf``
+.. |rndc_key| replace: ``/etc/rndc.key``
+.. |named_conf| replace: ``/etc/named.conf``
+.. |bind_keys| replace: ``/etc/bind.keys``
+.. |named_pid| replace: ``/run/named.pid``
+.. |session_key| replace: ``/run/session.key``
+"""