perf data with spaces appear to cause problems with 1.5.0

[tmuncks]

The perf string 'power level' appears to cause problems with Check_MK Raw 1.5.0 (p16 and p18 at least):

2019-06-24 10:22:50,077 [40] [cmk.web 125727] Failed to parse perfdata 'power level=-6.2;-9.5:-3.0;-13.5:1.0;; deviation=-0.1;-1.0:1.0;-2.0:2.0;;'
Traceback (most recent call last):
  File "/omd/sites/nuki/share/check_mk/web/htdocs/metrics.py", line 562, in parse_perf_data
    varname, values = part.split("=", 1)
ValueError: need more than 1 value to unpack
2019-06-24 10:22:53,036 [40] [cmk.web 125579] Failed to parse perfdata 'power level=-6.5;-19.0:-3.0;-23.0:1.0;; deviation=0.0;-1.0:1.0;-2.0:2.0;;'
Traceback (most recent call last):
  File "/omd/sites/nuki/share/check_mk/web/htdocs/metrics.py", line 562, in parse_perf_data
    varname, values = part.split("=", 1)
ValueError: need more than 1 value to unpack
2019-06-24 10:22:53,040 [40] [cmk.web 125579] Failed to parse perfdata 'power level=-6.2;-9.5:-3.0;-13.5:1.0;; deviation=-0.1;-1.0:1.0;-2.0:2.0;;'
Traceback (most recent call last):
  File "/omd/sites/nuki/share/check_mk/web/htdocs/metrics.py", line 562, in parse_perf_data
    varname, values = part.split("=", 1)
ValueError: need more than 1 value to unpack
2019-06-24 10:25:29,430 [40] [cmk.web 125727] Failed to parse perfdata 'power level=-0.9;-19.0:-3.0;-23.0:1.0;; deviation=0.1;-1.0:1.0;-2.0:2.0;;'
Traceback (most recent call last):
  File "/omd/sites/nuki/share/check_mk/web/htdocs/metrics.py", line 562, in parse_perf_data
    varname, values = part.split("=", 1)
ValueError: need more than 1 value to unpack
2019-06-24 10:25:29,439 [40] [cmk.web 125727] Failed to parse perfdata 'power level=0.4;-19.0:-3.0;-23.0:1.0;; deviation=0.1;-1.0:1.0;-2.0:2.0;;'
Traceback (most recent call last):
  File "/omd/sites/nuki/share/check_mk/web/htdocs/metrics.py", line 562, in parse_perf_data
    varname, values = part.split("=", 1)
ValueError: need more than 1 value to unpack

The result seems to be that devices using the plugin does not graph properly - even for unrelated services it seems.