Don't check RPM DB for BuildRequires pkgs if we are on --no-boostrap

If rpmbuild finds BuildRequires in SPEC file it queries RPM DB to
make sure package is available. Disable dependency check by passing
--nodeps option to rpmbuild if we are on --no-boostrap option.
cmsBuild scheduler takes care that all previous tasks (fetch, build,
install) are completed before launching build-* task, which has
Requires and BuildRequires dependencies. RPM DB is empty if we are
on --no-bootstrap.

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>