[Apache v2] Load apacheconfig tree and gate related tests (#7710)

* Load apacheconfig dependency, gate behind flag

* Bump apacheconfig dependency to latest version and install dev version of apache for coverage tests

* Move augeasnode_test tests to more generic parsernode_test

* Revert "Move augeasnode_test tests to more generic parsernode_test"

This reverts commit 6bb986ef78.

* Mock AugeasNode into DualNode's place, and run augeasnode tests exclusively on AugeasNode

* Don't calculate coverage for skeleton functions

* clean up helper function in augeasnode_test

tools/dev_constraints.txt

@@ -3,7 +3,7 @@
 # Some dev package versions specified here may be overridden by higher level constraints
 # files during tests (eg. letsencrypt-auto-source/pieces/dependency-requirements.txt).
 alabaster==0.7.10
-apacheconfig==0.3.1
+apacheconfig==0.3.2
 apipkg==1.4
 appnope==0.1.0
 asn1crypto==0.22.0

tools/oldest_constraints.txt

@@ -39,7 +39,7 @@ pytz==2012rc0
 google-api-python-client==1.5.5
 
 # Our setup.py constraints
-apacheconfig==0.3.1
+apacheconfig==0.3.2
 cloudflare==1.5.1
 cryptography==1.2.3
 parsedatetime==1.3