error when generate the software context

[Yongqin Liu]

If the adb connection is lost during the test, then the getting of software context will failed.
There is following information in http://validation.linaro.org/lava-server/scheduler/job/21339/log_file

WARNING: Could not read board information
WARNING: Could not read memory information
ERROR: Test execution error: ValidationError: Object has incorrect type (expected string) object_expr='object.test_runs[0].software_context.image.name', schema_expr='schema.properties.test_runs.items.properties.software_context.properties.image.properties.name.type')