Real /proc/cpuinfo files do not contain empty lines at the start
or at the end of file.

Signed-off-by: Kir Kolyshkin <[email protected]>

Since Linux kernel 3.8-rc1 (commit b4b8f770eb10a "ARM: kernel:
update cpuinfo to print all online CPUs features", Sep 10 2012)
the kernel does not print "Processor" as the first line of
/proc/cpuinfo. Instead, it adds a line named "model name"
with similar contents.

Fix the code for this case, and add more tests.

Signed-off-by: Kir Kolyshkin <[email protected]>

The `Features` line is the same for all CPUs, and yet it is assigned to
and parsed many times.

Optimize the code so it is only parsed once and assigned in place.

Signed-off-by: Kir Kolyshkin <[email protected]>

Avoid double check of each line for ":" -- since we're splitting the line anyway,
we can reuse the result.

This also prevents a potential panic of referencing non-existen field[1]
in case input contains a ":" with no space after.

Signed-off-by: Kir Kolyshkin <[email protected]>

Instead of reading the data to the buffer, then making a reader and a
scanner out of that buffer, let's analyze the data as we read it line by
line.

Signed-off-by: Kir Kolyshkin <[email protected]>

In case the input can't be read, scanner.Scan() stops and the code is
supposed to check for error using scanner.Err(). Do that.

In other words, instead of returning half-read cpuinfo, return an error.

Signed-off-by: Kir Kolyshkin <[email protected]>

There is no sense to skip empty lines at the beginning of the file since
there are none (there were in test data but it is fixed by an earlier
commit).

Logic is simpler now.

Signed-off-by: Kir Kolyshkin <[email protected]>