Flux fixes

[jnichols-git]

Fixing some errors that I left in the Flux implementation. Queries should now properly parse from the request body for POST requests (idiomatic for flux), and should use the OPC if there's no timestep, which is now parsed out of the first window() or aggregateWindow() found in the query, since using different timesteps for data in the DeltaProxyCache is probably bad.

Running some tests with InfluxDB 2.0 locally and will undraft once that's done and confirmed OK.

[coveralls]

Pull Request Test Coverage Report for Build 7073340712

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• 152 of 222 (68.47%) changed or added relevant lines in 8 files are covered.
• 165 unchanged lines in 11 files lost coverage.
• Overall coverage decreased (-0.4%) to 92.374%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/backends/influxdb/handler_query.go	25	28	89.29%
pkg/backends/influxdb/flux/flux.go	0	8	0.0%
pkg/backends/influxdb/flux/parser.go	38	47	80.85%
pkg/proxy/params/params.go	25	34	73.53%
pkg/backends/influxdb/model/unmarshal.go	30	71	42.25%

Files with Coverage Reduction	New Missed Lines	%
pkg/proxy/engines/document.go	1	99.51%
pkg/backends/influxdb/model/unmarshal.go	2	72.92%
pkg/routing/routing.go	3	98.29%
pkg/proxy/proxy.go	8	76.6%
pkg/backends/influxdb/flux/parser.go	10	86.23%
pkg/backends/options/options.go	11	97.05%
pkg/proxy/engines/proxy_request.go	11	93.75%
pkg/proxy/ranges/byterange/range.go	18	92.53%
pkg/proxy/handlers/purge.go	19	0.0%
pkg/proxy/engines/cache.go	30	92.06%

Totals
Change from base Build 4545767614:	-0.4%
Covered Lines:	17298
Relevant Lines:	18726

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💛 - Coveralls