Log NLSML as XML text rather than obj.inspect
Log NLSML as XML text rather than obj.inspect

See https://github.com/adhearsion/adhearsion/issues/563#issue-89313278

Converts this:
```
[2015-06-18 14:41:14.300] DEBUG AdhearsionASR::PromptBuilder: Ask completed with result #<AdhearsionASR::Result status=:match, confidence=0.89, utterance="goodfellows", interpretation="other", nlsml=#<Nokogiri::XML::Element:0x34e6198 name="result" namespace=#<Nokogiri::XML::Namespace:0x351167c href="http://www.ietf.org/xml/ns/mrcpv2"> children=[#<Nokogiri::XML::Element:0x34f826c name="interpretation" namespace=#<Nokogiri::XML::Namespace:0x351167c href="http://www.ietf.org/xml/ns/mrcpv2"> attributes=[#<Nokogiri::XML::Attr:0x3510fc4 name="grammar" value="http://10.203.175.51:8080/documents/ca6aea09628ee9d4d2797890ca599fa8">, #<Nokogiri::XML::Attr:0x3510fb0 name="confidence" value="0.89">] children=[#<Nokogiri::XML::Element:0x3501e48 name="input" namespace=#<Nokogiri::XML::Namespace:0x351167c href="http://www.ietf.org/xml/ns/mrcpv2"> attributes=[#<Nokogiri::XML::Attr:0x3519d68 name="mode" value="speech">] children=[#<Nokogiri::XML::Text:0x3519408 "goodfellows">]>, #<Nokogiri::XML::Element:0x3501a38 name="instance" namespace=#<Nokogiri::XML::Namespace:0x351167c href="http://www.ietf.org/xml/ns/mrcpv2"> children=[#<Nokogiri::XML::Text:0x35019d4 "other">]>]>]>>
```

Into this:
```
[2015-06-18 14:41:14.300] DEBUG AdhearsionASR::PromptBuilder: Ask completed with result #<AdhearsionASR::Result status=:match, confidence=0.89, utterance="goodfellows", interpretation="other", nlsml='<?xml version="1.0"?> <result xmlns="http://www.ietf.org/xml/ns/mrcpv2">   <interpretation grammar="http://10.203.175.51:8080/documents/ca6aea09628ee9d4d2797890ca599fa8" confidence="0.89">     <input mode="speech">goodfellows</input>     <instance>other</instance>   </interpretation> </result>'>
```
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