Increase default console ring allocation size and reduce default verbosity

Increase default console ring allocation size and reduce default verbosity

In order to have better chance that relevant messages fit into the
ring buffer, allocate a dynamic (larger) one in more cases, and make
the default allocation size depend on both the number of CPUs and the
log level. Also free the static buffer if a dynamic one was obtained.

In order for "xm dmesg" to retrieve larger buffers, eliminate
pyxc_readconsolering()'s 32k limitation resulting from the use of a
statically allocated buffer.

Finally, suppress on x86 most per-CPU boot time messages (by default,
most of them can be re-enabled with a new command line option
"cpuinfo", some others are now only printed more than once when there
are inconsistencies between CPUs). This reduces both boot time (namely
when a graphical console is in use) and pressure on the console ring
and serial transmit buffers.

Signed-off-by: Jan Beulich <jbeulich@novell.com>