Adds a trap for SIGTERM in entrypoint script

[dougbtv]

In my tests this improved the time to kubectl delete pod $multus-daemonset-pod -n kube-system by 5 seconds.

@s1061123 -- I had to use wait instead of read -- if I use sleep $x & read it waits for input before continuing, there is one spot where we sleep infinity, however, in a number of other spots we sleep inside a loop.

[coveralls]

Pull Request Test Coverage Report for Build 552395876

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 70.797%

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Totals
Change from base Build 521026319:	0.0%
Covered Lines:	1137
Relevant Lines:	1606

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💛 - Coveralls

[s1061123]

@dougbtv in the case of read, you just use read, without sleep. So we could use read at the last sleep infinite.

Other cases we still use sleep <n> & wait

[s1061123]

LGTM, thanks!