Format issues embedded in macros for two g1 source files

After adding the format attribute (for gcc and clang compilation, at least) in 8037816, two files in the G1 sources had format problems where the intended output could not be reverse-engineered. They were not likely to be crash-inducing, so the checks were disabled and the problem pushed to this bug.

The two files are:
src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp

Format checking is disabled with this macro near the top of each file; commenting it out (as seen below)

#if !defined(__clang_major__) && defined(__GNUC__)
// FIXME, formats have issues. Disable this macro definition, compile, and study warnings for more information.
// #define ATTRIBUTE_PRINTF(x,y)
#endif

leads to dozens of warnings about argument type, too many arguments, and use of '+' with a %s format.
Some of these are trivial point fixes, but some are also embedded in formatting macros.