bitbake: build: Ensure addtask before/after tasknames have prefix applied

"addtask do_XXX before YYY after ZZZ "

where YYY or ZZZ is missing the "do_" prefix don't work as expected. Ajust the
code so that it doesn't just silently do the wrong thing but works as expected.

Expand a test case to cover this.

(Bitbake rev: 21670b9bb8936ec44aedff26163948bbc2ceb44a)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/tests/parse.py

@@ -188,6 +188,9 @@ addtask do_mytask3
 deltask do_mytask3# comment
 deltask do_mytask4 # comment2
 
+# Ensure a missing task prefix on after works
+addtask do_mytask5 after mytask
+
 MYVAR = "do_patch"
 EMPTYVAR = ""
 deltask do_fetch ${MYVAR} ${EMPTYVAR}
@@ -198,7 +201,8 @@ deltask ${EMPTYVAR}
         f = self.parsehelper(self.addtask_deltask)
         d = bb.parse.handle(f.name, self.d)['']
 
-        self.assertEqual(['do_fetch2', 'do_patch2', 'do_myplaintask', 'do_mytask', 'do_mytask2'], d.getVar("__BBTASKS"))
+        self.assertEqual(['do_fetch2', 'do_patch2', 'do_myplaintask', 'do_mytask', 'do_mytask2', 'do_mytask5'], d.getVar("__BBTASKS"))
+        self.assertEqual(['do_mytask'], d.getVarFlag("do_mytask5", "deps"))
 
     broken_multiline_comment = """
 # First line of comment \\