Add notes about bashate E006 exception

bashate tests fail with 'E006: Line longer than 79 columns'.

As many scripts are deployed as templates and use jinja templating,
this rule is very difficult to achieve. It is still considered a
preference and should be a goal to improve readability, within reason.

Validation of this reasoning will be up to the human reviewers instead
of being forced by the lint tests.

Change-Id: I59cedad79814d51b7dc20610ee2eae38d7a83906

doc/source/developer-docs/scripts.rst

@@ -110,7 +110,11 @@ Testing may be done locally by executing:
 Bash coding conventions are tested using `Bashate`_, with the following
 convention exceptions:
 
-* E003: Indent not multiple of 4 (we prefer to use multiples of 2)
+* E003: Indent not multiple of 4. We prefer to use multiples of 2 instead.
+* E006: Line longer than 79 columns. As many scripts are deployed as templates
+        and use jinja templating, this is very difficult to achieve. It is
+        still considered a preference and should be a goal to improve
+        readability, within reason.
 
 Testing may be done locally by executing:
 

tox.ini

@@ -55,7 +55,8 @@ commands =
   # Run bashate check for all bash scripts
   # Ignores the following rules:
   #     E003: Indent not multiple of 4 (we prefer to use multiples of 2)
-  #     E006: Line longer than 79 columns
+  #     E006: Line longer than 79 columns (as many scripts use jinja
+  #           templating, this is very difficult)
   bash -c "grep --recursive --binary-files=without-match \
     --files-with-match '^.!.*\(ba\)\?sh$' \
     --exclude-dir .tox \