Refactor DB_POOL lazy static to account for namespaces for test runner #1343

Job	Run time
check	41s
audit	21s
clippy	1m 19s
test	2m 52s
rustfmt	7s
cross-mips64	49s
cross-mipsel	48s
cross-armv7	1m 0s
cross-aarch64	44s
cross-mips	1m 8s
cross-mips64el	39s
integration-test-five-nodes	24m 40s
legacy_integration-test	24m 16s
legacy_integration-test-with-backcompat	30m 28s
integration-test-debts	23m 10s
integration-test-eth-payments	21m 32s
integration-test-althea-payment	26m 56s
	2h 41m 30s

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