Add better error message with has trouble downloading parts of the SDK.

[yogurtearl]

Using version b182b51 ( master ):

Trouble downloading parts of the SDK should result in some "Error" level log, that says something about

Failed to fetch URL https://dl.google.com/android/repository/addons_list-2.xml, reason: Connection to http://localhost:9090 refused

Right now, we only get DEBUG logs.

13:27:10.655 [LIFECYCLE] [com.jakewharton.sdkmanager.internal.PackageResolver] Compilation API android-22 missing. Downloading...
13:27:11.560 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real] Refresh Sources:
13:27:11.564 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Fetching https://dl.google.com/android/repository/addons_list-2.xml
13:27:11.765 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Failed to fetch URL https://dl.google.com/android/repository/addons_list-2.xml, reason: Connection to http://localhost:9090 refused
13:27:11.765 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Fetched Add-ons List successfully
13:27:11.765 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Refresh Sources
13:27:11.765 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Fetching URL: https://dl.google.com/android/repository/repository-10.xml
13:27:11.783 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Failed to fetch URL https://dl.google.com/android/repository/repository-10.xml, reason: HttpHostConnect Connection to http://localhost:9090 refused
13:27:11.783 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Fetching URL: http://kindle-sdk.s3.amazonaws.com/addon.xml
13:27:11.785 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Failed to fetch URL http://kindle-sdk.s3.amazonaws.com/addon.xml, reason: HttpHostConnect Connection to http://localhost:9090 refused
13:27:11.788 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real] Refresh Sources:
13:27:11.788 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Fetching URL: https://dl.google.com/android/repository/repository-10.xml
13:27:11.807 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Failed to fetch URL https://dl.google.com/android/repository/repository-10.xml, reason: HttpHostConnect Connection to http://localhost:9090 refused
13:27:11.807 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Fetching URL: http://kindle-sdk.s3.amazonaws.com/addon.xml
13:27:11.809 [DEBUG] [com.jakewharton.sdkmanager.internal.AndroidCommand$Real]   Failed to fetch URL http://kindle-sdk.s3.amazonaws.com/addon.xml, reason: HttpHostConnect Connection to http://localhost:9090 refused