Increasing timeout for test.

With additional OpenGL checks, vtkRenderingOpenGLCxx-TestTextureSize  now takes
longer than 90s on certain machines (dash3). Increasing the timeout to 300s
which is typical for dashboards.

Change-Id: Iac4f5ff3f9eb22d3af1caf7507a162c7fa6cce05
Merge topic 'fix_dashboard_issues' into master

4b20f9b1 Increasing timeout for test.