Use more general names for user-customizable env variables

[critzo]

Three env variables currently exist that are configurable by people using Murakami whose contents are used to name test results files, and are saved as metadata fields in the test results themselves:

• MURAKAMI_SETTINGS_LOCATION
• MURAKAMI_SETTINGS_NETWORK_TYPE
• MURAKAMI_SETTINGS_CONNECTION_TYPE

Generalize these names across the application so users may logically define them based on their desired measurement focus. For example:

• MURAKAMI_SETTINGS_DEVICE_ID
• MURAKAMI_SETTINGS_DEVICE_METADATA1
• MURAKAMI_SETTINGS_DEVICE_METADATA2