Unity project having PackageManager component installed fails to open when disconnected from the internet.

Steps to reproduce:

1. Open Unity Editor.
2. The select existing project which contains PackageManager component.
3. Disconnect the internet.

Notes:
1. A popup appears with the message "Failed to resolve packages"
2. On selecting "Retry" popup appears again after sometime
3. On selecting "Continue" popup closes but nothing happens
4. On selecting "Quit" closes the popup and unity

Reproducible on: 2018.1.0b13, 2018.1.0b12, 2018.1.0b11, 2018.1.0b5

Note: Package Manager is introduced in 2018.1.0b5

Environment:
Windows 10, Windows7, Mac 10.13, 10.12