ovs-bugtool: Ability to collect the number of rotated logs.

ovs-bugtool: Ability to collect the number of rotated logs.

A big reason for a large debug bundle size is the size of log
files. By default we collect 20 rotated logs for each logfile.
Most of the times we collect the debug bundle as soon as we
hit a bug. In such cases, we know that we need only one day's
worth of logs.

This patch adds an option, '--log-days' to ovs-bugtool wherein
we can specify how many days worth of rotated logs do we need
as part of the debug bundle.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>