Fix SCTX-1776, CA-133656: iops is always (nearly) zero

Problem: The iops values are always or at least nearly zero

Root Cause: rrdd_plugin_iostat query those values from /sys/block/tdX/stat.
It treated the 1st (zero-based) and 5th columns as the the io-read-requests
and io-write-requests values. However, according to
https://www.kernel.org/doc/Documentation/block/stat.txt, 1st/5th are
io-read-merged and io-write-merged and 0th/4th are io-read-requests and
io-write-requests.

Solution: Revise the indices.
Merge commit '5f23bcf07373ad98df8af57ef2b44f27b39528e7'
CA-138835: rrdd plugins should exit on sigterm/sigint

Otherwise the main loop catches the signal and continues running, and
the init script eventually has to send SIGKILL.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #8 from johnelse/ca-138835

CA-138835: rrdd plugins should exit on sigterm/sigint
rrdp_iostat: push the exception handler for listing a domain's VBDs inwards

No functional change; refactoring only.

(cherry picked from commit 51be2a8498d1aebb5aa70c21d8a4cb42de0ae898)

Imported-by: John Else <john.else@citrix.com>

Conflicts:
	rrdp_iostat.ml
CA-141867: Look in both /local/domain/0/backend/vbd and vbd3 when listing a domain's VBDs

tapdisk2 uses vbd, tapdisk3 uses vbd3, so the domain's VBDs could be in either.

(We might have looked up the correct backend path for each VBD from the frontend
info, but we can't trust that a malicious frontend might not manipulate that
info.)

(cherry picked from commit b8d0fa35c4db464ac7b25a88d6f6dbb9183246f5)

Imported-by: John Else <john.else@citrix.com>

Conflicts:
	rrdp_iostat.ml
Merge pull request #11 from johnelse/ca-141867-master

CA-141867: Look in both /local/domain/0/backend/vbd and vbd3 when listing a domain's VBDs
Remove references to common Makefiles

These files aren't used, and don't exist in mock-land.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #12 from johnelse/remove-common-file-refs

Remove references to common Makefiles