add node wallet password environment variable

[Alesfatalis]

automatically unlocks node wallet if password is set

closes #323

[coveralls]

Pull Request Test Coverage Report for Build 7351269548

• 0 of 50 (0.0%) changed or added relevant lines in 8 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.4%) to 53.3%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core/src/metrics.rs	0	3	0.0%
core/src/scans.rs	0	3	0.0%
core/src/cli_commands/bootstrap.rs	0	4	0.0%
core/src/main.rs	0	4	0.0%
core/src/oracle_config.rs	0	5	0.0%
core/src/node_interface.rs	0	8	0.0%
core/src/node_interface/node_api.rs	0	10	0.0%
core/src/api.rs	0	13	0.0%

Files with Coverage Reduction	New Missed Lines	%
core/src/api.rs	1	0.0%
core/src/main.rs	1	0.0%

Totals
Change from base Build 7324796062:	-0.4%
Covered Lines:	2003
Relevant Lines:	3758

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💛 - Coveralls

[ross-weir]

Looking good, few small suggestions