title: Reinstall conan requires from conanfile.py
body: <p>Can I somehow automatically specify in conanfile.py install the required package even if it is already installed?
  If I do <code>conan install &lt;package&gt;</code> with my hands, then it will install it, even if it was installed before. But in conanfile.py it just writes &quot;: Already installed!&quot; and goes on.</p>
  <p>This may <code>conan create &lt;package&gt; --&lt;param&gt;</code>, but it would be better if it was written in the recipe itself.</p>
  <p>Thanks in advance</p>