execd processor does not handle newline characters in strings

[M0rdecay]

Actual behavior:

If the external processor returns data in the influxdb format in several lines, a parsing error occurs:

2020-09-08T12:00:39Z E! [processors.execd] Parse error: metric parse error: expected tag at 1:65: "some data here"

Additional info:

The situation is well described here - #7461
But now it occurs in the execd processor

[ssoroka]

Should be easy enough to resolve. Will take a look at it