recipetool: add setvar subcommand

Add a recipetool subcommand "setvar" to set a variable in a file. This
uses our existing logic such that it doesn't matter if the variable is
already set in the recipe, if it's set in the recipe or some inc file,
and if the variable is not currently set that the line setting the
variable gets inserted in the right place in the file.

Implements [YOCTO #7676].

(From OE-Core rev: 7c33ef77fa165182d24f0a9ae769e9e630e6bd47)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/recipetool

@@ -34,7 +34,7 @@ plugins = []
 def tinfoil_init(parserecipes):
     import bb.tinfoil
     import logging
-    tinfoil = bb.tinfoil.Tinfoil()
+    tinfoil = bb.tinfoil.Tinfoil(tracking=True)
     tinfoil.prepare(not parserecipes)
     tinfoil.logger.setLevel(logger.getEffectiveLevel())
     return tinfoil
@@ -96,7 +96,9 @@ def main():
 
     try:
         if getattr(args, 'parserecipes', False):
+            tinfoil.config_data.disableTracking()
             tinfoil.parseRecipes()
+            tinfoil.config_data.enableTracking()
         ret = args.func(args)
     except bb.BBHandledException:
         ret = 1