siggen: Remove fsync that is causing performance issues

This fsync was added for belt and braces protection for things like sstate
on NFS. To be honest, it probably doesn't buy much, if the rename isn't
atomic, all bets are off anyway and there are bigger issues to worry about.

The issue is that at the end of every task, the dump_sig() code is triggered
to save out information about the task and this was triggering an fsync(fd).

Whilst it may select the file descriptor, on file systems like ext4, it will
require large parts of the journal to be written out so it can have
significant impact. latencytop showed an average fsync() call overhead of about
2s and if that happens for 5000 tasks, the time mounts up. This blocks the next
task execution by that time.

We therefore drop the fsync since in reality its causing problems and is unlikely
to buy much.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
fetch2: Don't allow '/' in user:pass, fix branch containing '@'

* currently decode_url regexp parses branch=@foo as username so it ends like this:
  - ('git', '', 'foo', 'git.openembedded.org/bitbake;branch=', '', {})
  + ('git', 'git.openembedded.org', '/bitbake', '', '', {'branch': '@foo'})
* http://hg.python.org/cpython/file/2.7/Lib/urlparse.py also assumes
  that there is at least one '/' as separator between netloc and path,
  params, so it looks reasonable to prevent including '/' in username

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
fetch2/gitsm: Use ud.basecmd instead of hardcoding git

This allows FETCHCMD_git to override the fetcher command as the git fetcher does.

[YOCTO #5717]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
SignatureGenerator: Add empty implementation for dump_sigs

* bitbake -S throws exception when 'noop' signature handler is used

[YOCTO #5738]

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>