perf trace: Fix comm resolution when reading events from file

perf trace: Fix comm resolution when reading events from file

Task comm's are getting lost when processing events from a file. The
problem is that the trace struct used by the live processing has its
host machine and the perf-session used for file based processing has its
host machine.  Fix by having both references point to the same machine.

Before:

     0.030 ( 0.001 ms): :27743/27743 brk( ...
     0.057 ( 0.004 ms): :27743/27743 mmap(len: 4096, prot: READ|WRITE, flags: ...
     0.075 ( 0.006 ms): :27743/27743 access(filename: 0x7f3809fbce00, mode: R ...
     0.091 ( 0.005 ms): :27743/27743 open(filename: 0x7f3809fba14c, flags: CLOEXEC ...
...

After:
     0.030 ( 0.001 ms): make/27743 brk( ...
     0.057 ( 0.004 ms): make/27743 mmap(len: 4096, prot: READ|WRITE, flags: ...
     0.075 ( 0.006 ms): make/27743 access(filename: 0x7f3809fbce00, mode: R ...
     0.091 ( 0.005 ms): make/27743 open(filename: 0x7f3809fba14c, flags: CLOEXEC ...
...

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1380395584-9025-4-git-send-email-dsahern@gmail.com
[ Moved creation of new host machine to a separate constructor: machine__new_host() ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>