build: touch files when extracting rpm tarballs

build: touch files when extracting rpm tarballs

Type: fix

- Long story short, intermittently centos jobs have been
  failing with clock skew issues. When someone commits a
  patch on a machine with the date ahead of UTC, then clock
  skew will be encountered when extracting the RPM source
  tarball. See [0] and [1] for details.

- Replace 'make bootstrap' with 'make install-dep' in
  RPM package build specfile.

[0] https://unix.stackexchange.com/questions/164807/does-git-archive-use-the-wrong-file-timestamp
[1] https://git.fd.io/vpp/tree/Makefile#n380

Change-Id: Iebfb9eb2e26c1f2e4488e871da86d0c60b9f4048
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>