Add make targets for fast linting and testing

Fast linting only needs modified files with pylint and diff with
pycodestyle. It's good enough to detect most code errors very fast. It
typically takes less than 10 seconds. A complete full pylint run uses
all CPU cores for several minutes. PEP 8 violations are typically
reported after 30 minutes to several hours on Travis CI.

Fast lintings uses git diff and git merge-base to find all modified
files in a branch or working tree. There is no easy way to find the
branch source. On Travis the information is provided by Travis. For
local development it's a new variable IPA_GIT_BRANCH in VERSION.m4.

Fast testing execute all unit tests that do not depend on ipalib.api.

In total it takes about 30-40 seconds (!) to execute linting, PEP 8 checks
and unittests for both Python 2 and 3.

Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

VERSION.m4

@@ -48,6 +48,16 @@ define(IPA_VERSION_PRE_RELEASE, )
 ########################################################
 define(IPA_VERSION_IS_GIT_SNAPSHOT, yes)
 
+########################################################
+# git development branch:                              #
+#                                                      #
+# - master: define(IPA_GIT_BRANCH, master)             #
+# - ipa-X-X: define(IPA_GIT_BRANCH,                    #
+#       ipa-IPA_VERSION_MAJOR-IPA_VERSION_MINOR)       #
+########################################################
+define(IPA_GIT_BRANCH, master)
+dnl define(IPA_GIT_BRANCH, ipa-IPA_VERSION_MAJOR-IPA_VERSION_MINOR)
+
 ########################################################
 # The version of IPA data. This is used to identify    #
 # incompatibilities in data that could cause issues    #
@@ -128,6 +138,7 @@ NEWLINE)) dnl IPA_VERSION end
 dnl DEBUG: uncomment following lines and run command m4 VERSION.m4
 dnl `IPA_VERSION: ''IPA_VERSION'
 dnl `IPA_GIT_VERSION: ''IPA_GIT_VERSION'
+dnf `IPA_GIT_BRANCH: ''IPA_GIT_BRANCH'
 dnl `IPA_API_VERSION: ''IPA_API_VERSION'
 dnl `IPA_DATA_VERSION: ''IPA_DATA_VERSION'
 dnl `IPA_NUM_VERSION: ''IPA_NUM_VERSION'