Specifying more than one explicit version results no experiments to be queued.

[vulder]

When trying to run an experiment on two version, explicitly specifying both results in nothing being queued. However, both on separate calles work.

> benchbuild -vv run -E GenerateBlameReport xz@869b9d1b4e xz@a3148c0446
Number of actions to execute: 1

Experiment: GenerateBlameReport


Summary:
1 actions were in the queue.
0 actions failed to execute.

This run took:    0.158 seconds.

> benchbuild -vv run -E GenerateBlameReport xz@a3148c0446
Number of actions to execute: 13

Experiment: GenerateBlameReport
 * echo: Start experiment: GenerateBlameReport
 * All required:
   * xz: Clean the directory: /home/vulder/vara-root/benchbuild/results/GenerateBlameReport/xz-c_projects@a3148c0446
   * xz: Create the build directory
   * echo: Selected xz with version a3148c0446
   * Project environment for: xz @ (Variant(version='a3148c0446'),)
   * xz: Compile
   * xz: Execute configured action.
   * xz: Execute configured action.
   * xz: Clean the directory: /home/vulder/vara-root/benchbuild/results/GenerateBlameReport/xz-c_projects@a3148c0446

> benchbuild -vv run -E GenerateBlameReport xz@869b9d1b4e
Number of actions to execute: 13

Experiment: GenerateBlameReport
 * echo: Start experiment: GenerateBlameReport
 * All required:
   * xz: Clean the directory: /home/vulder/vara-root/benchbuild/results/GenerateBlameReport/xz-c_projects@869b9d1b4e
   * xz: Create the build directory
   * echo: Selected xz with version 869b9d1b4e
   * Project environment for: xz @ (Variant(version='869b9d1b4e'),)
   * xz: Compile
   * xz: Execute configured action.
   * xz: Execute configured action.
   * xz: Clean the directory: /home/vulder/vara-root/benchbuild/results/GenerateBlameReport/xz-c_projects@869b9d1b4e