Vendor el8 dependencies

[hopkiw]

On el8 more of the dependencies have to be vendored, including cachetools and rsa. Since there's no longer a simple transform command, move the packaging to use native sources and patches instead. The package build script will have to have a one line change to include these files in RPMDIR/SOURCES directory before invoking rpmbuild.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hopkiw

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[google-oss-robot]

@hopkiw: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
prow/presubmit/packagebuild	324bd4014dbe65325d85b4bd9d8a06acc803cc40	link	/packagebuild

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[hopkiw]

package build is expected to fail for el7

[illfelder]

/lgtm