Extended printf test with new mixed format cases (#1988)

According to work plan from issue #1058

Added new case `TYPE_MIXED_FORMAT_RANDOM` which focus on three factors:

-data before conversion flags - this is randomly generated ascii string
-randomly generated conversion flags - integer or floating point, for
each flag specific argument is generated
-data after conversion flags - this is randomly generated ascii string

Moreover, due to fact in case of `TYPE_MIXED_FORMAT_RANDOM` test is
generated on the fly, logging of negative result was extended.

test_conformance/printf/test_printf.h

@@ -58,6 +58,7 @@ enum PrintfTestType
     TYPE_FORMAT_STRING,
     TYPE_VECTOR,
     TYPE_ADDRESS_SPACE,
+    TYPE_MIXED_FORMAT_RANDOM,
     TYPE_COUNT
 };