check for problematic value range

A common problematic practice is, to declare the value parameter
with the same FloatRange than the target. Because of measurement
errors, a value might be near, but outside the limit.
In order to avoid this, we force the programmer to declare a
bigger range for the value than for the target, or to
explicitly disable this check on a module property.
It is also fine to declare the value without limits.

This behavior may be disabled via command line option or in the
general config file. For simplicity, FloatRanges inside data
structures are not considered.

+ above command line option is also used to disable the error
  handling on a string to float conversion
+ log appropriate error message for string to float conversion

Change-Id: Ib78ea1fb7c821442bf5847030573c8c27822dea5
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27574
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_datatypes.py

@@ -28,7 +28,8 @@ import pytest
 from secop.datatypes import ArrayOf, BLOBType, BoolType, \
     CommandType, ConfigError, DataType, Enum, EnumType, FloatRange, \
     IntRange, ProgrammingError, ScaledInteger, StatusType, \
-    StringType, StructOf, TextType, TupleOf, get_datatype
+    StringType, StructOf, TextType, TupleOf, get_datatype, \
+    DiscouragedConversion
 from secop.lib import generalConfig
 
 
@@ -677,5 +678,5 @@ def test_lazy_validation(dt):
     generalConfig.defaults['lazy_number_validation'] = True
     dt('0')
     generalConfig.defaults['lazy_number_validation'] = False
-    with pytest.raises(ValueError):
+    with pytest.raises(DiscouragedConversion):
         dt('0')