misc: optimize append_lines_to_file() to reuse remote.write_file
misc: optimize append_lines_to_file() to reuse remote.write_file

The misc.append_lines_to_file method has been using get
remote file to temporary file and then write back to
remote host.

The orchestra.remote.write_file method has 'append' parameter
when using which there is no data downloaded from remote host.

Signed-off-by: Kyr Shatskyy <82d0c7561ff7e9a20a19db22e8fb5b2adaa3d71e@suse.com>

dmick/teuthology,ceph/teuthology,dmick/teuthology,SUSE/teuthology,ktdreyer/teuthology,ktdreyer/teuthology,ceph/teuthology,dmick/teuthology,SUSE/teuthology,SUSE/teuthology