Develop info-/error-message printing library functions, support log-level for messages.

[gapisback]

A recent PR #162 has introduced a large collection of diffs of this nature:

-    printf("Executable read failed\n");
+    printf("%s() error, line %d, Executable read failed\n",
+         __func__, __LINE__);

The change itself is useful for improved troubleshooting.

However, we need a flexible interface that can be applied to all places where such messages are printed.
Some ideas: (which were aired out & discussed with CC-core dev team before logging this issue)

• Synthesize other caller-info in the form: %s:%d::%s(), passing-in __FILE__, __LINE__, __func__, so that we consistently see the 3-part code location identifier
• Support some form of info / message log-level
• Provide a way to print either to stdout, stderr, or to some log file / output stream.

Study existing implementations for this kind of interface and under this issue, prototype a set of initial changes that support this functionality. Work-up an implementation in few typical places, to see how the usability aspects are.

Once the base interfaces and accepted and finalized, actual roll-out and implementation in the entire Certifier code base will be done in follow-on PRs.